Contaminant resistant gear pumps and motors with wear inserts

ABSTRACT

Hydraulic equipment useful as a pump or motor intended for applications where hydraulic fluid is exposed to contamination by abrasive particulate material is disclosed. Leakage paths from the high pressure chamber in a gear pump or motor are provided with inserts of an abrasion and erosion resistant material at points where wear from abrasives in the hydraulic fluid is aggravated. In particular, the bearing surfaces of the pressure loaded side plates are provided with an insert of abrasion and erosion resistant material in the mesh region of the teeth. Erosion and abrasion resistant rings are located on the side plates in the region surrounding the openings for the shafts and extending interiorly of the tooth root circle to the journal bearings. 
     Also disclosed are radial sealing shoes which are supported by the side plates and are radially urged into sealing relationship with the tips of the teeth by the pressure existing at the high pressure side of the gears.

FIELD OF THE INVENTION

The invention relates to improvements in hydraulic equipment such asgear pumps and motors and more particularly to improvements whichincrease the suitability of high performance gear pumps and motors foruse in working environments wherein large amounts of abrasiveparticulate materials are present.

RELATED APPLICATIONS

This application is related to application Ser. No. 29,891 filed Apr.13, 1979, now U.S. Pat. No. 4,266,195 issued May 12, 1981 in the name ofJames M. Eley and James R. McBurnett and owned by the assignee of thisapplication.

BACKGROUND OF THE INVENTION

Hydraulic equipment, and in particular high performance pumps and motorsused in applications where there is a large amount of particulatecontaminant material are found to be subject to an unusually high degreeof wear. The problem is particularly troublesome in underground miningoperations where maintenance is difficult to accomplish and equipment isfrequently run on a round-the-clock basis. Not infrequently, hydraulicpumps will last no longer than about three months due to wear caused bythe presence of highly abrasive particulate contaminants in thehydraulic fluid. The particulate contaminants in the hydraulic fluidabrade and erode critical sealing surfaces within the pumps and motorsand at the end of a relatively short time, volumetric efficiency hasdropped to the point where the pump or motor is very inefficient. Thisoperating inefficiency, among other things, leads to overheating of thehydraulic fluid and eventually to failure of the pump. Because theoccurance of such failures is relatively unpredictable and inspectionand monitoring of pump efficiency is not easily carried out,particularly in underground mines, the practice has developed to simplyreplace the hydraulic pumps and motors at relatively short intervals inorder to avoid problems.

Significant reductions in wear due to contaminated hydraulic fluid areachieved through the use of gear pumps and motors constructed inaccordance with the teachings of copending application Ser. No. 29,891.In that application a construction is disclosed in which radiallymovable sealing elements provide a sealing surface with the tips of thegear teeth adjacent the high pressure port of the pump or motor. Theseelements are pressure compensated to eliminate slippage caused by wearat the tips of the teeth by maintaining a good seal with the tips of theteeth despite wear which may occur due to the presence of contaminantsin the hydraulic fluid.

Another leakage path in gear pumps and motors is between the sides ofthe teeth and the side walls of the pumping chamber. It is known in theprior art that the side walls should be comprised of pressurecompensated plates which are pressed against the sides of the teeth byfluid pressure which is communicated against the outsides of the platesfrom the high pressure side of the pump or motor.

Another type of leakage path which is aggravated at high pressuresexists in certain regions of the pressure plates interfacing with thegears where there is an abrupt transition from high to low pressure.

One such leakage path exists at the surface of the plates bounding themesh region of the gears. Where the gears mesh there is a point ofcontact which moves along a path termed the path of contact which is thedemarcation line between high and low pressures. Although there islittle or no leakage between the teeth when the gears are rotating, thepoints along this line at the boundaries of the teeth have beendiscovered to be natural leakage paths in which the pressure plates aresubjected to a higher degree of wear and abrasion than the rest of theirsurface. So far as we can determine, the prior art contains no solutionto the problem other than careful maintenance and avoidance of oilcontamination by use of filters or the like.

The other point where a large pressure drop may exist is between theroot circle of the gears and the shaft bearings. Although the existenceof this leakage path has been recognized, where journal bearings havebeen employed it has been considered to be necessary for lubrication ofthe bearings or at least an expedient solution to the lubricationproblem.

Even though the side plates are pressure compensated so as to keep theside plates pressed against the sides of the teeth despite wear of theside plates, they are still susceptible to damage by abrasive anderosive action of contaminants in the hydraulic fluid in the sealingarea between the root circle of the teeth and the shafts on which thegears are mounted.

The susceptibility to damage of the type to which this invention relatesis attributable to the fact that the surface of the pressure plateadjacent the teeth must be selected primarily for its ability to act asa bearing for the sides of the gear teeth which normally move at veryhigh velocities. Available materials (primarily bronzes) that make goodload bearing surfaces are relatively soft and offer little resistance toabrasive and erosive attack by particulate contaminants. As indicatedabove, pressure compensation of the side plates is a substantialsolution to the problem of wear between the sides of the teeth and thepressure plate. However, it has been discovered that pressurecompensation does not provide a solution to wear of the side plate inthe teeth mesh region or interiorly or beneath the root circle of theteeth and in fact these areas are the ones most susceptible to damage bycontaminants in gear pumps or motors.

Various other approaches to the problem of erosion and abrasion at theroot circle are currently in use. One approach is to increase the rootseal, thereby reducing the amount of leakage by increasing the distancebetween the root circle and the outside diameter of the gear shaft. Theproblem with this approach is that it can only be accomplished byreducing shaft diameter which leads to bearing failure or by increasingthe overall size of the gears which also means an increase in the sizeof the pump housing and an appreciable increase in weight and in cost.Another approach has involved the pressurization of the ends of thehousing so that there is no flow of oil into the bearing region.Attendant with this approach is an increase in the cost of the housingor a risk of increased pressure failure. Shaft sealing problems are alsomore difficult. Pressure compensation of the side plates is moredifficult to accomplish due to difficulties in isolating high and lowpressure regions at the back of the side plates. The bearings requiredfor such applications must be roller or needle bearings.

SUMMARY OF THE INVENTION AND OBJECTS

The invention involves the use of a novel design of side plate whereinregions of abrupt transition from high to low pressure on the surfacesof the side plates, which regions are not pressure compensated, areformed of an erosion and abrasion resistant material.

An important objective of the invention is the provision of an improvedform of pressure compensated side plate construction in which thesources of pressure plate wear referred to above are substantiallyreduced.

A more particular objective of the invention is the provision ofabrasion and erosion resistant inserts in the mesh regions and the rootseal regions of the pressure plate.

Still another objective of the invention is the reduction of wear andprolongation of life of gear pumps and motors used in environments wherelarge amounts of particulate contaminants exist.

Still another objective of the invention is the provision of means ingear pumps and motors for maintaining high volumetric efficiency over arelatively long period of time.

In summary, the foregoing and various other objectives of the inventionare achieved by the provision in a gear pump of pressure compensatedside plates having an abrasion and erosion resistant material in thearea of the plate immediately adjacent the gear shafts and extendingradially outwardly to include the root circle of the gear teeth. Anabrasion and erosion resistant insert is also disposed in the plates inthe region adjacent the mesh region of the teeth.

The foregoing and other objectives and advantages of the invention willbecome apparent upon reference to the following detailed description ofa preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an exterior view of a typical hydraulic gear pumpincorporating the principles of the present invention with a portion ofthe house broken away for illustrative purposes;

FIG. 2 is a section view taken on line 2--2 of FIG. 1;

FIG. 3 is a section view taken along line 3--3 of FIG. 2;

FIG. 4 is a detailed view of a side pressure plate incorporating theprinciples of the present invention;

FIG. 5 is a section view taken on line 5--5 of FIG. 4 and;

FIG. 6 is a detailed sectional view of a side plate and the mesh regionof the gears in a pump constructed according to the prior art;

FIG. 7 is a sectional view taken on line 7--7 of FIG. 6;

FIG. 8 is a detailed sectional view of a side plate constructedaccording to the present invention;

FIG. 9 is a sectional view taken on line 9--9 of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made to FIGS. 1 through 3 which show a gear pump inwhich a pair of gears 10 and 11 are provided as pumping elements forpumping hydraulic fluid from a reservoir to a hydraulically operateddevice not shown. Gears 10 and 11 are mounted on parallel shafts 12 and13, best shown in FIG. 2 and preferably journalled within sleeve typebearings 12a and 13a within a housing 14. The housing is typicallydivided into 2 or more components, a three piece housing comprised ofparts 14a, 14b, and 14c, being illustrated. The three components aresecured together by suitable means such as bolt 16.

As can be seen in FIGS. 1 and 2, shaft 13 projects out of the housingand is provided with a splined drive connection 17 forming a part of adrive means which also includes a prime mover, not shown.

An inlet line or passage represented at 18 in FIG. 1 and a portion boredat right angles at 19 leads to the hollow pumping chamber 20 withinwhich the gears are mounted as best illustrated in FIG. 3. An outletpassage comprising portions 21 and 21a leads to the hydraulicallyoperated equipment, not shown.

The sides of the pumping chamber 20 within which the gears are mounted,are defined by side plates 15 more fully described hereinafter and shownin more detail in FIGS. 4 and 5. A preferred form of plate constructionis shown in detail in FIGS. 4 and 5. The side plates fit within thehousing and are designed to bear against the sides of the gear teeth.

As is best shown in FIG. 3, the interior of the housing is formed sothat there is a substantial clearance space between the tips of the gearteeth at the addendum circle as shown at 10a and 11a, and the innerperiphery of the housing well as shown at 22. This clearance space runsfrom the inlet region 19 circumferentially of each gear to a point atwhich radial sealing means are located adjacent the outlet 21. Thedistance between the teeth tips and the wall 22 on the low pressure sideof the gears is such that under all anticipated load conditions theteeth do not contact the wall.

The radial sealing means preferably comprise shoes 23 which areseparated for independent positioning adjacent each side of the outlet.Preferably the shoes 23 float within a semicircular recess machined intothe housing 14b so as to extend across the entire face of the gears. Theshoes extend at each end beyond the inner borders of the pressure platesand are dimensioned so that the pressure plates provide the sole supportfor the shoes which float within the semicircular recess. As can best beseen in FIG. 3 each is provided with a curved surface 24 whose radius isequal to the radius of the curved edge surfaces of the pressure plates.

When mounted within the recess, the shoes are separated by a space 25which provides for communication between the gears and the dischargeopening 21. Preferably, a pin 25a is mounted within one of the shoes andextends towards the opposite shoes so as to maintain the shoes in properposition when the pump is not operating. When the pump is operating aslight clearance is maintained between the bottom of the pin and theadjacent surface of the other shoe. In order to confine and limit theextent to which the discharge pressure is applied to the shoes, the backof each shoe is provided with a flexible sealing member 26 which ismounted in a recess 27 extending lengthwise of the shoes. The ends ofthis sealing member overlap the ends of sealing members 28 which fitwithin grooves in side sections of the housing 14a and 14c, to definesealed pressure regions behind the shoes and the side plates. It can beseen from FIG. 3, that the discharge pressure is communicated to thisregion behind the shoes as limited by the seals 26 and the seals in theside sections and acts to press the shoes against the edges of the sideplates and into sealing relationship with the tips of the teeth.Preferably, the shoes are dimensioned when initially made so that whenthe pump is finally assembled, the gears track into the shoes slightly,cutting their final clearance, and thus assuring a good seal between theteeth and the shoes.

The discharge pressure is also communicated to the backs of the sideplates within the confines of seal 28, the pressure balance on theplates being such that a seal is maintained with the sides of the teethdespite wear at the interfaces of the plates and the teeth.

Preferably the side plates have champhered portions 29 which are locatedadjacent to and in position so that they slightly overlap the shoes.These portions serve to provide a more gradual, less abrupt buildup ofpressure as the teeth pass into sealing relationship with the shoes.

As should be evident from the above, the function of the shoes is toprovide a fluid seal with the tips of those teeth 10a and 11a in thelimited region immediately adjacent the high pressure side of the gears,which in the case of the pump is the outlet 21. As is shown in FIG. 3,these sealing shoes subdivide the interior of the housing into arelatively large inlet chamber portion which extends from inlet port 19to the point where the teeth tips engage the surface of a shoe 23wherein the fluid pressure is substantially zero and a relatively smalloutlet chamber portion wherein the pressure is the full dischargepressure.

Although the sealing surface of the shoes 23 can be made longer than isshown in FIG. 3, the preferred length of the sealing surface of eachshoes is such that the tips of no more than two teeth at any given timeare in full sealing relationship with the sealing surface of the shoes.In operation, this means that the full discharge pressure is limited inits application to the area of those teeth immediately adjacent theoutlet. This pressure acts to push the shoes apart as viewed in FIG. 3and also acts against the backs of the shoes within the limits of thespace defined by seals 26. The net effect is to press the shoes intosealing relationship with the teeth. It should be noted that the fluidpressure in the cavity between any two teeth in sealing relationshipwith the elements 23 is at an intermediate value somewhat below thedischarge pressure whereas the remainder of the cavity 20 whichencompasses over two-thirds of the circumference of the gears is at lowpressure.

Turning now to the construction of the side plates 15, the plates arepreferably constructed of a hardened steel back portion 30 with a bronzelayer 31 on the side adjacent to the gear teeth. Each plate 15 ispreferably bored and counterbored and provided with an insert ofhardened steel or other abrasion and erosion resistant material. Therings, shown at 32 in FIGS. 4 and 5 are secured mechanically againstmovement as by press fitting into the counterbored recesses of the sideplates although in certain circumstances the rings may be made integralwith the plates. The internal diameter of each ring is selected so as toclear the gear shafts. The external diameter of the rings must be atleast equal to and preferably is slightly greater than the root circlegears 10 and 11. It is important that the hardened steel rings notextend appreciably beyond the root circle, due to the relatively highcoefficient to friction of the steel as compared with that of the bronzebearing surface. It has been found that the friction effects existingbetween the side plates and the region of the gears extending from theoutside diameter of the shaft to the root circle of the teeth are notappreciable whereas the frictional forces generated if the entiresurface of the side plates were to be made of hardened steel would be sogreat as to cause overheating and a substantial shortening of the lifeof the pump or motor.

Other material than hardened steel may be employed, the criterion beingthat the material be resistant to the abrasive and erosive forces of theparticulates likely to be encountered. Steel having a hardness of 40-45Rockwell C produces excellent results.

Although the hardened steel rings are preferably press fitted into thecounterbored openings in the side plates, it should be understood thatif desired these rings could be secured with a swaging tool or be madeintegral with the hardened steel back portion of the side plates.

As shown in FIG. 4, a hardened steel insert or button 33 is alsoprovided in each plate in the region adjacent the mesh area of theteeth. In the preferred form of invention this insert extends throughthe plate and is secured thereto by having its end 33a upset.

FIG. 6 shows a wear plate constructed in accordance with the prior art,illustrating the effects of abrasion and erosion along the line ofaction of the gear teeth, As shown in FIG. 6, particulate in the oilabrades and erodes a channel in the bronze bearing material of the sideplate. The reason for this is further illustrated in FIG. 7 which showsa pair of meshing teeth on gears 10 and 11. The edges of these teeth areeither initially formed with a slight radius or are quickly worn to aslight radius during use, so that at the point of contact as shown at 34in FIG. 7 a leakage path is formed through which particulate laden oilflows at very high pressure. The action of this oil very quickly formsthe diametrrically shaped groove illustrated in FIG. 6. FIGS. 8 and 9are views identical to FIGS. 6 and 7 except that the position of insert33 is illustrated. Even though a small passageway still exists at theedges of the gear teeth as shown at 34, the wear resistant insert 32prevents enlargement of this path and appreciable change in volumetricefficiency of the pump or motor.

In summary, in both instances, the abrasion and wear resistant materialis provided within the pump or motor at a region where a relativelylarge pressure drop exists.

In the case of the rings 32, the region just exteriorly of the toothroot circle is at a higher pressure than the portion of the housingcontaining the bearings. Erosion and abrasion resistant rings are notemployed. Particulate material carried by the oil abrades a passagewayfrom the root circle to the shaft along the bearings 12a and 13a. Sincethis wear is not pressure compensated, the passage becomes progressivelylarger as more and more flow of particulate-laden material to thebearing drain takes place. The use of the abrasive resistant material inthis region substantially eliminates this problem.

At the mesh area of the teeth, there is also an abrupt transition from ahigh pressure at one side of the mesh area to a low pressure at theother side. Separation of fluid between the side plates causes a higherdegree of abrasion and erosion in this area than in the rest of theplate as a whole and this excess erosion is not adequately compensatedfor by the pressure acting on the back of the side plates. The presenceof the hardened steel plates or buttons 33 substantially eliminate theproblem of erosion and abrasion at this point.

Although the abrasion and erosion resistant side plates of the presentinvention are useful in gear pumps which do not have radially movableshoes, the combination or radially movable shoes and abrasive anderosive resistant side plates drastically reduces problems arising fromthe use of contaminant-laden fluids. Conventional pumps equipped withwear resistant rings and inserts have been shown to have a life at leastfive times the life of pumps not so equipped when run with fluid ladenwith contaminants. Pumps equipped with wear resistant rings, inserts andradially sealing shoes have been shown to have a life of at least fourtytimes that of pumps not so equipped. Pumps using the invention areparticularly well suited for use in mining applications. A spark-freematerial such as cast iron can be used for the housing, the materialsfor the shoes and the major portion of the sealing surface of the sideplates can be made of bronze whereas those areas subjected to greatestattack from abrasion and erosion can be made of hardened steel.

What is claimed is:
 1. In hydraulic equipment of the gear type havingintermeshing gears, a housing for the gears, gear support shafts withinsaid housing and journal bearings supporting said shafts for rotationwithin said housing, bearing drain passages in said housing formaintaining said journal bearings at a relatively low pressure, a pairof floating pressure plates on opposite sides of said gears, said platesbeing mounted for movement axially of the shafts towards the sides ofsaid gears, said plates having a flat surface of bronze or like bearingmaterial on the plate side which faces said gears to form a bearingsurface therewith, means for communicating the high pressure operatingfluid to the sides of the plates which face away from the gears to urgethe plates into sealing relationship with the sides of the gears, eachplate having a pair of openings sized to provide clearance for the gearshafts, an insert of abrasion and erosion resistant material recessedwithin each opening, said inserts being secured against movement withrespect to the plates and extending axially of the shafts from the platesides facing the gears to the ends of the journal bearings and furtherextending radially from points adjacent the circumference of the gearshafts to the root circle of the gear teeth.
 2. In equipment accordingto claim 1, further including a piece of abrasion and erosion resistantmaterial inlaid in the bearing surfaces of each of said pressure plates,said pieces being flush with the bearing surface and each beingdimensioned to cover the path followed by the point of contact of themeshing gear teeth.
 3. Equipment according to claim 2, wherein saidpiece has a portion extending through the plate, and further whereinsaid portion is secured to the plate.